In the field of gas turbine technology a great deal of effort has been, and continues to be, directed toward improving thermodynamic efficiency by operating gas turbine engines at ever increasing temperatures. These temperatures may exceed the temperatures that some materials within the turbine engine structure can normally tolerate. As such, cooling air may be provided to various turbine engine components using cooling air extracted from other parts of the engine. For example, in some gas turbine engines cooling air is extracted from a plenum at the discharge of the compressor, and is then directed to certain portions of the turbine.
For some gas turbine engines, the air that is extracted from the engine for turbine cooling may be at temperatures that require the air to be cooled before being directed to the turbine. In some turbofan gas turbine propulsion engines, a portion of the fan air flowing in the bypass duct may be continuously redirected and used to cool the extracted turbine cooling air. During some operational levels of the turbofan engine, fan air is not needed to adequately cool the extracted air, resulting in parasitic losses.
Hence, there is a need for a system that will ensure the flow rate of redirected fan air is sufficient to adequately cool air that is extracted for turbine cooling air, while substantially reducing, if not eliminating, parasitic engine losses. The present invention addresses at least this need.